1. Field of the Invention
The present invention relates to carburetors for small internal combustion engines of the type used with lawn mowers, lawn tractors, sport vehicles, and other small working implements.
2. Description of the Related Art
Small internal combustion engines typically include a carburetor for providing an air/fuel combustion mixture to the engine. One type of carburetor commonly used in small engines includes a fuel bowl for storing fuel and a throat with a venturi region. Intake air is drawn through the throat to generate a reduced pressure in the venturi region, drawing fuel from the fuel bowl into the throat where the fuel mixes with the intake air to form the combustion mixture.
In order to start the engine, the carburetor must be primed so that an enriched air-fuel mixture is initially supplied to the engine. Typically, the air space in the fuel bowl is pressurized to force an amount of priming fuel from the fuel bowl directly into the throat to provide an enriched air/fuel mixture for engine starting.
One primer system includes a resilient primer bulb or bellows that, when manually depressed, increases the pressure in the fuel bowl, causing an amount of priming fuel to flow from the fuel bowl through a nozzle into the carburetor throat. In some of these systems, the primer bulb also serves as a check valve to seal off an internal vent passage within the carburetor, such that air within the primer bulb is directed only into the fuel bowl.
However, if the operator does not depress the primer bulb completely, the resulting pressure in the fuel bowl may be inadequate to cause a sufficient amount of fuel to flow into the throat. In addition, the primer bulb is most effective as a check valve when it is depressed directly inwardly toward the carburetor along a straight line. If the operator depresses the bulb at an angle, the bulb may not effectively seal off the internal vent passage, allowing air to leak into the internal vent passage such that the fuel bowl is not pressurized sufficiently to provide priming fuel to the carburetor throat in an amount effective for engine starting.
A number of other primer systems use a primer bulb to introduce liquid fuel directly into the carburetor throat. In these systems, fuel is drawn into the primer bulb when the primer bulb is depressed and then released. When the primer bulb is depressed again, the fuel contained in the primer bulb is forced from the primer bulb into the throat. This system poses similar disadvantages. If the primer bulb is not depressed completely, the fuel injected from the primer bulb to the throat may be insufficient to start the engine.
It is desired to provide a primer system for small engine carburetors that is an improvement over the foregoing.